Safety switches of this type are known in many embodiments, also being referred to as control switches and/or signaling apparatuses. They are used in control panels, lifts, machines etc. for actuating electrical control systems. In potentially dangerous situations, actuating the safety switch causes the relevant circuits to open or close. Reference can be made to documents DE 199 60 695 A1 and DE 41 01 493 C2 as known examples.
A safety switch of this kind comprises a switch head having a plunger (as the actuation means) which is mounted in a housing wall in a receptacle opening. The longitudinal axis of the safety switch lies perpendicularly to the plane of the housing wall. The safety switch is mounted from the inner side of the housing wall using a threaded ring. The plunger of the safety switch is designed and installed such that upon actuation thereof (from the inoperative position) into the switch position, it acts upon contacts of a switch module by means of an actuation stroke. The essential function of the safety switch consists in the fact that, upon actuation (pushing in, pressing in), it influences the contacts of the switch module in such a way that an OFF switch function and/or a warning function occurs. The safety switch is most often used for an emergency off function, and therefore the safety switch is also referred to as an EMERGENCY OFF button. The actuation of the safety switch can be associated with a lock in the OFF switch position (in particular in an EMERGENCY OFF circuit).
EP 2525378 A1 discloses a safety switch, the housing of which is designed in such a way that it has a closure means which can be opened or removed only by means of unauthorized access (using mechanical force). Unauthorized access to the housing is therefore immediately recognizable.
In the case of pressure-actuatable safety switches there is the problem of incorrect assembly of the switch head and the switch module or unauthorized separation of the switch head and the switch module not being recognizable from the outside. Such a separation can occur by destruction of the assembly or by unauthorized access (tampering) to the assembly. The actuation of the switch head would not have any effect in such situations. The desired monitoring signal of the safety function is assumed to be absent.
EP 01906418 A1 discloses a safety switch having a monitoring function. In this safety switch too, upon actuation of the actuation means (plunger), contacts of a switch module are actuated (as known) by means of an actuation stroke, a switch block of the switch module being designed as a signaling switch block. When the safety switch is correctly mounted, the switch block which is designed as a signaling switch block is permanently actuated by means of an actuation pin. By means of this monitoring function which is achieved using the signaling switch block, a fault can be monitored in which the signaling switch block is detached from the housing wall using the actuation means mounted therein. The signaling switch block alters its switch state once it is more than a certain distance away from said housing wall, as a result of which a fault signal is emitted.
As mentioned, in the case of this safety switch one of the switch blocks is provided with a control function so that the switch block having the control function is excluded for other switch functions.